Unusual functions of cheap parts

LED's work both ways, as a light emitter and a photodiode.

The inbuilt colour filter can be used to distinguish between Grass and Not grass f.ex. by comparing output from a red and a green LED using white light as illumination.

Back when fiber was ex$$$pensive one often saw clever circuitry using two transmitters to form a duplex connection over a single fiber.

The USD 10 solar powered garden lamps will, with a little persuation, yield a nice solar cell well below the price of a similar unit in the shops - and - two 600 mAh NiMh batteries and a grotty circuit for switching the LED.

Also a photodetector that is insensitive to long wavelengths (because of the high bandgap).

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John Devereux

Hello John,

I wrote: NOT PIN - Diodes - as they wouldn't snap.

i mean Band Switching diodes for TV-Tuners like the BA244 and the BA682.

BA682 Datasheet:

- and they snap! Try it!

Jorgen dj0ud

2N2369 for fast pulses. 2N2222 and even 2N2219 works, but a bit slower and they requiring more voltage to avalance, but still < 1nS rt The Zetex are slower but can deliver much more current (up to 60A, ZTX 415 family).

Jorgen

As an addition to the various mentions of common diodes as varactors there is a well publicized British design for a frequency tripler that will put out 2 watts at 1.3 GHz and uses five 1N914's in parallel.

I once built an HF transceiver that used CMOS logic chips for all functions except an audio low noise amp and a voltage regulator...with further thought those two could likely be done with CMOS logic too.

And by varying the reverse bias through a current source (or moderately large fixed resistor) you can make them into nifty phase shifters.

Jim

"Henry Kiefer" skrev i en meddelelse news:4385b3b1$1$27887$ snipped-for-privacy@newsread4.arcor-online.net...

Unbuffered logic gates can make a really bad but still useful analogue amplifier by adding feedback and bias.

I got that!

OK, I'll try some.

Thanks

John

There's also an LM35 in a TO-220 package! Ideal way to monitor a heatsink.

John

The problem is that the carbon rod conducts heat quite well, so after a while, any wooden object will catch fire :-).

You must have quite slow fuses in 110 V land if you can do a reliable ignition without blowing the fuse. For 230 V operation, I would suggest using a current limiting resistor (such as a large heater) or an inductance (such as fluorescent light ballast) during the ignition. When there is a solid arc, the current limiter can be shorted out.

Paul

Our newspaper had an article on that. Also, for model rockets, burning up an ordinary resistor can be used as a super-cheap ignitor. Best--- Ron

I

diode,

diode.

another

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tell us more John

NT

Aren't you in danger of damaging your eyes from the UV emitted from the arc?

Roy Lewallen, W7EL

I would put a 100 watt lamp in series thereby limiting the current. I would shave the ends down to points so they heated up rapidly. I put them into a hollowed out fire brick and made a cheap furnace. Of course don't look at it; it's like looking at the sun.

PS: I was 16 at the time ;-)

hi,

sorry if you didnt like everything, but sometimes some voilence against parts that cost you half a day of time and gave you a bad headache while troubleshooting is necessary...

For more useful things, FETs actually can work as quite useful one-component HF oscillators if wires and connection points are properly chosen.With a second transistor one can build a working shortrange AM transmitter.

A rather useful (works perfectly for SMPS uses) AC current probe for a scope can be made by using a small UI cored RFI filter coil from a monitor, connecting its windings in series and terminating with a 1ohm resistor, to which a coax cable with BNC connector is soldered to. The wire you want to measure the current in simply is fed trough the core one time. This only gives quantitative measurements unless calibrated but can be very useful if you cant afford a real current probe.

The known resonant royer circiut used for CCFL inverters can be used for larger inverters if appropriate parts are chosen, and can produce some high frequency/high voltage with a transformer from a old TV (with no internal rectifier). This has its uses, besides connecting it to a old light bulb that works as plasma globe or connecting both outputs to a large neon bulb [Bienenkorbglimmlampe], which simply looks very nice but also produces lots of RFI, so dont run it for too long.

FET gate drivers make nice TTL output stages for function generators, as these can drive rather high currents and are fairly robust.

If a slowly, steadily changing linear voltage is necessary (for ex. confirming the linearity of something) a 10turn precicion pot copuled with a slow syncronous motor (a old microwave oven has a nice 2.5u/min one) by some tape (so it slips/breaks when the pot is at its endpoint) works nicely.

The current limiter I saw used a glass pie pan with pieces copper metal on each side with salty water as the electrolyte. It would start to steam some when in operation. The furnace was a small clay flower pot with holes in each side with the carbon rods sticking inside until they touched.

As a boy, I used an electric teakettle as a ballast for a two-D-cell carbon arc lamp--worked great.

Cheers,

Phil Hobbs

I used a 0.5 or 0.7 mm pencil lead gently torqued down across the terminals of a regulated DC power supply. Set the current limit very low, crank the voltage up all the way and increase the current limit until the center of the lead starts glowing red. Due to the heatsinking effect of the binding posts, the lead will always heat up the most in the center, then the carbon will start to evaporate and the remaining lead will gradually neck down in the center until it is glowing white hot. As soon as the lead breaks in the middle, you convert from incandescent to carbon arc lamp, which usually surprises everybody watching. The arc is good for about 5 seconds until the voltage drop across the arc exceeds the capability of the power supply.

I have also seen thermistors used as a self regulating thermal element for a crystal oven.

Joe Leikhim K4SAT "The RFI-EMI-GUY"

"Follow The Money"

Pooh Bear wrote:

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Joe Leikhim K4SAT
"The RFI-EMI-GUY"

"Follow The Money"